Boiler Heat Pump

Boiler Heat Pump with Ice Storage Unit

The aim of the funded project "Zeolite: a mineral for energy-efficient heating and cooling" was to develop a technology to succeed condensing appliance technology. An energy-efficient heating system was developed within the framework of the project for heating rooms and service water. The system is a combination of a condensing boiler (current state-of-the-art) and a solid sorption heat pump powered by a gas burner with the environmentally-compatible pairing of water and zeolite. This boiler system of the future will heat and cool at the same time!


This innovative boiler heat pump is characterised by the following features:

  • Energy-saving compared to the current state-of-the-art is 25%; at high warm water temperatures of 60…70 °.
  • Thanks to the combination of a boiler heat pump and an ice storage unit, the system requires around 75% less heat from the environment than an electric heat pump.
  • Ambient heat can be provided by simple technical means, e.g. with solar collectors, even in winter; the utilization of heat from waste water and waste air is also possible.
  • Flue gases can be cooled to below 0 °C. With the new boiler heat pump system, more pollutants can be separated from the resulting flue gas than with conventional condensing boilers.
  • There is the option of extending the system to form a gas-powered room air-conditioning system. It is not necessary to provide any significant amount of electrical power to run the air-conditioning system.
  • The system is very easy to maintain and has a long service life.
  • Cost savings thanks to the use of small ambient heat exchangers.
Zeo-Tech constructed prototypes of a 10 kW boiler heat pump with an ice storage unit and subsequently conducted measurements and optimised the design.

Photo of the first prototypes


Funded by the Deutsche Bundesstiftung Umwelt (German Federal Foundation for the Environment)

Operating phases of the boiler heat pump

Heating phase (desorption)



During desorption, the zeolite filling in the sorber is heated by means of direct gas firing until the adsorbed water is forced out of the zeolite in the form of vapour. The water vapour flows to the coldest part in the system, i.e. in the vicinity of the closed cold vapour damper, where it condenses thereby passing on condensation heat to the recirculated heating water. Condensation accumulates when the cold vapour damper is closed.

The pre-heated heating water is then heated further in a sorber heat exchanger with a through-flow of hot waste gas before it flows to the radiators in the home in the heat pipe. Once the zeolite filling in the sorber has been regenerated and all of the desorbed water vapour is above the cold vapour damper in the form of condensate, the gas burner is shut down (stand-by mode).

The heating water is now heated by the perceivable heat in the sorber.


Cooling phase (adsorption)
The cooling phase begins by adjusting the waste gas dampers in the sorber so that the hot gases circulate in the sorber, driven by the fan, and heat the heating water in the sorber heat exchanger and then, having cooled down, flow through the hot zeolite filling.

Before the sorber can cool down to below approx. 80 °C as a result of the heat exchange process with the heating water, the cold vapour damper is opened by means of an electromechanical mechanism so that the cold condensate can run into the ice storage unit (evaporator). The adsorption process begins and the adsorption heat that is generated in the zeolite is once again transferred to the heating water. At the same time, ice is formed again in the evaporator. The proportion of ice in the water/ice mixture in the evaporator therefore fluctuates depending on the operating status of the system.

The cold "generated" in the evaporator can also be used for cooling or air-conditioning with the aid of ambient heat exchangers.

When the adsorption heat is no longer sufficient to heat the heating water to around 80 °C, the gas burner is started up once more and the waste gas dampers are adjusted so that hot waste gas is largely piped through the zeolite filling in the sorber for the purpose of regeneration (desorption). The cold vapour damper is closed and the heating phase described above begins anew.